1. Field of the Invention
The present invention relates to a metal nanoparticle dispersion, and more particularly, to a metal nanoparticle dispersion capable of suppressing spreadability at room temperature and a drying phenomenon at heating temperature.
2. Description of the Related Art
Recently, a high-density, highly integrated printed circuit board has been required with an increasing demand for light, thin, short and small electronic equipment. In the case of the printed circuit board, used wires have to have their fine line width and pitch. As one of methods for embodying this fine circuit wire, a single-step inkjet printing process rather than a conventional complicated photolithographic process has been actively studied. The single-step inkjet printing process has an advantage in that its manufacturing process is very simple since an inkjet pattern is directly printed onto a substrate, and therefore the manufacturing cost is extraordinarily low.
Metal nanoparticle dispersions having a high boiling point and low viscosity are widely used in the inkjet printing method to embody a fine metal wire. A metal nanoparticle dispersion having low viscosity is desirable in consideration of the ejectability from an inkjet head, but, when the metal nanoparticle dispersion is ejected onto a substrate, it may be difficult to form a wire having fine line width due to the low viscosity of the metal nanoparticle dispersion. Viscosity of the metal nanoparticle dispersion generally depends on the viscosity of a dispersion solvent, and therefore there has been an attempt to adjust the viscosity of the metal nanoparticle dispersion by controlling the characteristics of solvents.
Therefore, a dispersion solvent, which has a high boiling point and low viscosity and shows its excellent dispersing property with respect to metal particles, is used for the metal nanoparticle dispersion for an inkjet ink so as to prevent the metal nanoparticle dispersion from being dried in an inkjet head nozzle and facilitate smooth flow of the metal nanoparticle dispersion. It has been known that the viscosity of the metal nanoparticle dispersion is preferably in a range of 20 mPa·s or less (at 20° C.), such that the metal nanoparticle dispersion has ejectability in a conventional piezo-type inkjet head.
Korean Patent Publication No. 2006-0060725 proposes a silver nanoparticle dispersion using tetradecane as a dispersion solvent. Since the dispersion solvent, tetradecane, has low viscosity of 2.0 to 2.3 mPa·s (at 20° C.), a high-concentration dispersion in which a content of silver nanoparticles is 60 wt % has low viscosity of approximately 8 mPa·s (at 20° C.). However, the silver nanoparticle dispersion including tetradecane has a disadvantage in that, since it takes several minutes to dry a wire, the deposited wire may be spread, which makes it difficult to form a fine wire.
Therefore, there has been a continuous demand for development of a metal nanoparticle dispersion that is able to control its characteristics such as viscosity by using a dispersion solvent that has excellent ejectability from an inkjet head and facilitates formation of a wire having a fine line width.